1. Field of the Invention
Embodiments relate to a semiconductor memory device and to a method of manufacturing the same. zMore particularly, embodiments relate to a phase change memory device and to a method of manufacturing the same by removing an upper portion of a capping layer on a phase change material layer before forming a contact hole through an insulation film on the phase change material layer.
2. Description of the Related Art
A semiconductor memory device may store data and may include volatile semiconductor memory devices, e.g., a Dynamic Random Access Memory (DRAM), a Static Random Access Memory (SRAM), and so forth, and nonvolatile semiconductor memory devices, e.g., a flash memory of NAND or NOR type based on an Electrically Erasable Programmable Read Only Memory (EEPROM).
The volatile semiconductor memory device may have fast input/output data operation, but the stored data may be lost by an interruption of power supply. Thus, the volatile semiconductor memory device may require a periodic refresh operation and a high charge storage capacity. For example, the DRAM may have a capacitor having a bottom electrode with an increased surface area to increase its capacitance. An electrode with an increased surface area, however, may reduce an integration degree of the DRAM.
The nonvolatile semiconductor memory device may maintain stored data even when power supply is interrupted, but data programming/erasing may require high operating voltage, as compared with power source voltage, for tunneling charges through a gate insulation layer. Thus, e.g., the flash memory device may require a boosting circuit for generating voltage necessary for the programming/erase operation. Use of a boosting circuit, however, may increase a design rule of the flash memory device.
Attempts have been made to make a semiconductor memory device capable of incorporating advantages of the volatile and nonvolatile memory devices, e.g., a semiconductor memory device having a high operational speed and a large capacity of memory storage. For example, a semiconductor memory device having a reduced power consumption and dominant data maintenance, e.g., Ferroelectric Random Access Memory (FRAM), Magnetic Random Access Memory (MRAM), Phase-change Random Access Memory (PRAM), nanofloating gate memory (NFGM), and so forth.
A PRAM may achieve a high integration with a low cost through a simplified structure and a high speed. Data storage in a PRAM may be obtained by using a resistance difference based on phase change of material from a crystalline state to an amorphous state, i.e., the phase change material may have a high specific resistance when at an amorphous state and a low specific resistance when at a crystalline state. Thus, logic information stored in a unit cell of the PRAM may be identified by sensing a difference of current amount flowing through the phase change material. The phase change may be controlled by adjusting an amount of heat applied to a phase change material, e.g., an amount of current and/or a length of time.
The conventional PRAM, however, may include a phase change material having a portion exposed to a contact hole formed subsequently. Such an exposure may cause defects to a contact plug formed in the contact hole due to fumes of the phase change material, thereby reducing reliability and production yield of the PRAM.